Wireless telephones, such as mobile/cellular telephones and cordless telephones, and other consumer audio devices, such as mp3 players, are in widespread use. Performance of such devices with respect to audio intelligibility can be improved by providing noise canceling using a microphone. In noise cancellation, the microphone measures ambient acoustic events and then inserts an anti-noise signal into the output of the device to cancel the ambient acoustic events measured by the microphone. The acoustic environment around personal audio devices can change dramatically, depending on the sources of noise that are present and the position of the device itself. An adaptive noise cancellation (ANC) system may be employed to adapt the noise canceling to take into account environmental changes. However, some drawbacks are associated with conventional ANC systems.
A conventional AEC system is illustrated in FIG. 1. An AEC system 112 in a device receives input from a microphone, which receives noise, speech, and echoes from each active speaker of the device. The AEC system 112 also receives input signals corresponding to the audio signal driving the active speakers, which are correlated with the echoes received by the microphone. The AEC system 112 uses the input speaker signals to remove echoes from the input microphone signal to generate an output audio signal. An adaptive filter is controlled through filter coefficients to decouple the far-end signal of the speakers from a near-end signal of the microphone.
The presence of signals in the input microphone other than the far-end speaker signal inhibits operation of the adaptive filter. For example, the presence of both a near-end talker and a far-end talker can disrupt adaptation of the filter. Conventionally, a detector of near-end speech, called a double-talk detector (DTD), is used to control the AEC to prevent this disruption. A DTD 114 is coupled to the AEC system 112 to provide an adapt enable signal. When the DTD 114 detects this double-talker scenario, the DTD 114 instructions the AEC system 112 to stop adaptation of the filter. This halting of adaptation prevents the filter from diverging. However, DTDs present several problems. DTDs are often unreliable in correctly detecting a double talker scenario. Additionally, DTDs only offer a binary control to turn on or off the adaptation of the filter based on whether double talk is present or not. Furthermore, DTDs do not detect near-end noise, which can also cause the AEC to diverge.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for acoustic echo cancellation (AEC) systems employed in consumer-level devices, such as mobile phones. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art. Furthermore, embodiments described herein may present other benefits than, and be used in other applications than, those of the shortcomings described above.